earth geoscience

1. EARTH AND CLIMATE
ASSIGNMENT
PRESENTED BY – JUHI RANI

2. WHAT WE ARE GOING TO CLEAR
THROUGH THIS PRESENTATION
• Why the average temperature on Earth has always been fluctuated in the
geological history?
• Why do we encounter glacial and interglacial periods ?
• The average temperature on Earth millions of years ago was 8 degrees
warmer than present? ( was it a global warming)
• Seasonal variation and climatic changes have been speeded up or it is at it’s
own pace?

4. How did the temperature differences arise?
• Solar radiation, volcanic activity may be one of the reasons of these climatic changes but it
is a very rare phenomenon.
• The main influence is of Milankovitch Cycles. They have driven Ice Ages in the geological
past.
• The variation of amount of sunlight received by Earth, orbital path all the factors together
hits the climate age.
• Man – made activities may have accelerated the climatic change but the climate change
phenomenon is a natural process.
• Even plate tectonics which leads to major disaster (earthquake, volcanism, tsunami) and also
change in the circulation of wind patterns may cause the change in temperatures.

5. MILANKOVITCH CYCLE
• In the early 1900s the Serbian Astronomer Milutin Milankovitch calculated several
cyclical changes in Earth’s orbit around the Sun, axial tilt and axial orientation.
• He postulated that these Milankovitch cycles that operate on the order of tens of
thousands of years may be responsible for cycles in climate, including glacial and
interglacial sequences.
• Milankovitch thought the temperature on Earth was influenced by 3 variables
related to the position of Earth relative to the Sun. As Sun is ultimate source of
heat and energy for the Earth.

6. • The types of Orbital variations –
• Eccentricity
• Axial Tilt
• Precession
These together are known as Milankovitch Cycles.

7. ECCENTRICITY
The circularity of Earth’s orbit around the Sun. Earth’s orbit is not centred on the Sun,
and the amount of eccentricity varies over time.
• At one extreme, the eccentricity cycle the Sun is at almost the exact centre of
Earth’s Orbit. At other extreme, earth is approximately 11 percent closer to the Sun.
• PERIHELION- The day of the year when Earth reaches its closest distance to the
Sun, that at its closest distance to the Sun, that at its opposite position 6 months
later-Aphelion.
• Eccentricity gradually changes from a more circular to a more elliptical orbit, with a
periodicity of approximately 95,000-1,00,000 years.

10. • INVERSE SQUARE LAW states that the intensity of radiation received by a
body is inversely proportional to the square of the distance between the
emitting and receiving body, this difference in distance results in Earth
receiving about 7 percent less insolation in July than it does in January.
• Periods of low eccentricity are more likely to coincide with glacial periods
within ice ages on Earth, whereas periods of high eccentricity are more likely
to be linked to interglacial phases.

11. TILT
The Earth’s axis is tilted from the vertical by 23.5°and that this angle of tilt does not
change through the course of the year. Milankovitch noted, however, that in reality on
geological time scales the tilt does slowly change in a cyclical fashion, from a minimum
of about 21.8° from the vertical to a maximum of about 24.4° from the vertical.
• The periodicity of this Milankovitch cycle is approximately 44,000 years.
• The cycle implies that the Tropic of Cancer and Tropic of Capricorn, which are
currently at 23.5°N and 23.5°S latitude, respectively, vary from about 21.8° latitude
to about 24.4° latitude.

13. • The cyclical changes in the angle of tilt affect the amount of summer to winter
contrast in heating, and, therefore, seasonality.
• The smaller the tilt, the closer to the equator the Sun’s direct rays remain throughout
the year. In periods of geological history when the tilt is relatively small, summers in
middle and high latitudes are cooler (all other factors being equal) but winters are
milder because the solar declination is not so far away in the opposite hemisphere.
Such situation encourages glaciation.
• By contrast, periods of high tilt allow the Sun’s direct rays to penetrate farther
poleward than average. This causes summer temperatures to be high, because the
solar declination approaches the midlatitudes more closely. But it also causes cold
winters, when the solar declination is farther away in the opposite hemisphere.

14. PRECESSION OF THE EQUINOXES
The —the changes in the direction that Earth’s axis points (but not the angle—which
represents tilt). Earth’s axis wobbles like a spinning top because Earth is not a perfect
sphere. Precession refers to this gyrating type of motion.
• The axis points in a varying direction about the same angle of tilt (although, as we
just saw, the tilt simultaneously undergoes cyclical changes) over time, with a
periodicity of approximately 23,000 years.
• A progressive change in the dates of the solstices, equinoxes, perihelion, and
aphelion occurs because of this Milankovitch cycle and because Earth’s elliptical
orbit itself is rotating.

16. COMBINED EFFECTS
• when all three of the above factors are in phase, such that they all point to a
warmer or colder Earth, the apexes of the glacial–interglacial sequence seem
to be reached.
• . Most climatologists believe that tropical areas do not show the climatic
fluctuations nearly as much as higher latitudes (i.e., Arctic amplification)
because changes in the cycles do not affect solar radiation receipt much in
those areas.

17. CLIMATE TIME MACHINE
• The small changes set in motion by Milankovitch cycles operate separately and
together to influence Earth’s climate over very long timespans, leading to larger
changes in our climate over tens of thousands to hundreds of thousands of years.
• Milankovitch combined the cycles to create a comprehensive mathematical model
for calculating differences in solar radiation at various Earth latitudes along with
corresponding surface temperatures. The model is sort of like a Climate Time
Machine. It can be run backward and forward to examine past and future climate
conditions.
• Milankovitch assumed changes in radiation at some latitudes and in some seasons
are more important than others to the growth and retreat of ice sheets.

18. THANK YOU!!